Increasing numbers of computer devices utilize data sharing, where a single file or other data unit is accessed and operated on by multiple computer devices. For example, data can be stored at server-side storage, including cloud storage. Multiple clients may have access to the data. Examples of commercially-available remote data services include the SIMPLE STORAGE SERVICE or S3, available from AMAZON WEB SERVICES LLC and the AZURE service available from MICROSOFT CORPORATION.
Data sharing schemes provide many advantages, including high availability, increased accessibility, data back-up, and a reduced need for local data storage hardware. On the other hand, increased access times for remote data storage lead to increased system latency and slower operation. Many systems address the latency issue utilizing local caching. According to local caching, clients maintain copies of files or other units of data at local storage. This increases the speed of read and write requests, but also creates complexity when more than one client or application attempts to read or write to the same data. Most servers address this issue by operating cache coherency schemes. According to cache coherency schemes, clients receive permission from a server to cache certain units of data. The server then manages situations where multiple clients attempt to cache the same unit of data simultaneously. According to one common cache coherency scheme, the server issues an operational lock (oplock), a lease, or other cache coherency mechanism to a client entitling the client to cache a unit of data and perform certain operations on the data. The extent of allowed operations (e.g., read, write, attribute, handle) are determined by the type of oplock issued. For example, when a first client performs an incompatible operation on a unit of data that is the subject of an existing oplock to a second client, the server may break the oplock with the second client.
According to existing network file systems, the client executes a network file system component to handle communication with the server as well as cache coherency. For example, when an application requests to read or write to a file, the request is forwarded from the application, to the operating system and ultimately to the network file system component. The network file system component communicates with the appropriate server to request any required oplocks or other cache coherency mechanisms and, if permitted, make the requested data manipulation. Many network file system implementations, however, do not permit cache coherency requests from components other than the network file system component.